1. Field of the Invention
The present invention relates to methods and apparatus for treating silicate substrate surfaces and, more particularly, textured quartz substrates.
2. Description of the Related Art
During most semiconductor manufacturing processes, such as dielectric etching or chemical vapor deposition, unwanted materials are sometimes formed on the interior surfaces of the processing chamber and on the chamber parts used in the manufacturing process. It is important that the materials deposited on the interior surfaces and chamber parts not become a source of contaminants that can flake, fall, or be knocked off and deposit upon a wafer that is being processed in the chamber. Such contaminants can damage the wafer, reducing the “yield” of usable devices.
For example, in dielectric etching long-chain carbon polymers may build up on the interior walls of the processing chamber. Loose particles of these polymers may break off during the manufacturing process and contaminate the wafers. Contaminants can cause high resistance, adhesion problems for subsequent layers, reduced insulation, and other performance and reliability subsequent layers, reduced insulation, and other performance and reliability problems.
Conventionally, processing chambers and parts are cleaned by manual scrubbing. In this conventional method, the manufacturing process is halted and the processing chamber opened such that the interior walls may be scrubbed. Sometimes, when manual scrubbing is not thorough enough, the yield of semiconductors subsequently processed will be greatly affected. Furthermore, scrubbing does not tend to be completely thorough, especially with high-surface area textured surfaces.
Other methods have been proposed to overcome problems with the conventional manual scrubbing method. One such method, which is applicable to removing oxide and dielectric contaminant build-up, involves the use of a plasma-enhanced etching process to “dry clean” the semiconductor processing parts. In that prior art method, fluorine-based gases such as CF4 and CHF3 and oxygen are highly energized to form a plasma which reacts with the contaminants to form CO2, SiF2 and other gaseous compounds which are then vacuumed away through the processing chamber's exhaust system.
One of the more common silicates used for chamber parts and surfaces is quartz (SiO2). For example, quartz domes are used to define the top portion of some semiconductor chambers, and quartz nozzles are used to inject gasses into semiconductor chambers. However, the prior art methodology is generally not well suited for cleaning processing chambers which include quartz substrates. Quartz parts and domes are frequently sent out to specialty cleaning houses or replaced, at considerable cost.
Quartz is usually manufactured with a smooth surface, e.g. having a roughness of about 16 Ra. However, contaminants which may be deposited on quartz of such smoothness during the semiconductor manufacturing process do not adhere well to the quartz surface, and are prone to becoming separated from the quartz surface and settling on the semiconductor wafer being processed. For this reason, quartz is often “textured” by increasing its surface area by, for example, roughening, to increase the adhesion or “stiction” of the contaminant layer on the quartz.
FIGS. 1A-1D illustrate a prior art roughening process 100 where a coarse grit 110 is projected at an angle 140 that is from 60-90° to the surface 120 of a substrate 130. If the angle is less steep than about 60°, the texturing process is considered to be too slow for most purposes. However, it has been found that grit-blasting at the high angles tends to create cracks 150 in the roughened surface. These cracks can cause pieces of the roughened surface to become a source of particle contaminants 160 by becoming dislodged from substrate 130, suca as illustrated in FIG. 1C. Such particle contaminants may introduce impurities in the wafers being processed, adversely affect yield. In addition, as illustrated in FIG. 1D, contaminants may adhere to the substrate surface over time and will eventually flake off or otherwise become dislodged from substrate 130 and fall in pieces 170 onto the wafers.
Therefore, what is needed is a method of forming a textured quartz substrate surface generates fewer cracks and other defects, and which reduces flaking or shedding of particulate matter, such as dust and other contaminants that have accumulated on the surface, while maintaining a high surface area. In addition, the shape and roughness of the surface should provide improved adhesive properties for holding on to such particulate matter during the course of semiconductor processing. Also needed are systems capable of forming such a substrate surface and a method and apparatus which is particularly applicable to remove polymer and photoresistive contaminant build-up on these surfaces such as quartz. It is further desirable to further increase the surface area of a textured quartz surface.